Overwash and overtopping
Overwash occurs when the flow of water of a breaking wave runs up the beach and overcomes the frontal dune. It normally transports sediment from the low-lying section of the beach to the dunes or to the environment inward. Apart from flooding and destruction, overwash can therefore contribute to significant imbalances in the coastal sedimentary equilibrium and cause important morphological changes along the coast. Overwash occurs mostly during periods when high energy waves, storm surge and high tides coincide. Overwash is one of the dominant mechanisms involved in barrier-islands landwards migration since they can transfer large amounts of sediment from the sea-facing flank of the barrier to its lagoon side, making the position of the barrier to be displaced landwards.
Overtopping occurs when the flow of water of a breaking wave runs up a coastal engineering structure like a port jetty, an oceanfront revetment or any type of hard coastal defence. Overtopping is therefore a serious threat to coastal engineering structures and to the property (ships, goods, equipment, buildings, vehicles) they protect as well to the life of those who live or work nearby.